System and method for monitoring environmental conditions

ABSTRACT

A system and method are disclosed for monitoring environmental conditions of a perishable product. The system includes an environmental sensor configured to sense one or more environmental conditions of the perishable product and an analog integrator in communication with the environmental sensor, the analog integrator being formed on a polymer substrate and including one or more tunable components. The system also includes a comparator in communication with the analog integrator and configured to change state when an output of the analog integrator reaches a selected threshold level, and a control module in communication with the comparator and the analog integrator. The control module is configured to control the operation of the analog integrator based on an output of the comparator.

PRIORITY INFORMATION

This application is a Divisional of U.S. patent application Ser. No.11/318,115 filed Dec. 23, 2005, now U.S. Pat. No. 7,641,973 which claimspriority to U.S. Provisional Patent Application No. 60/639,117, filedDec. 24, 2004, the disclosures of which are incorporated herein byreference in its entirety. A notice of allowance with regard to thepreceding application was mailed on Aug. 5, 2008.

BACKGROUND

Embodiments of the present disclosure relate generally to methods andapparatus for monitoring temperature, humidity, and/or otherenvironmental or chemical analog variables. More particularly, althoughnot exclusively, these embodiments are concerned with the detection ofproduct abuses such as spoilage and/or the detection of the level offreshness or environmental abuses of products, equipment or consumableitems.

As an introduction to the problems solved by the present application, itis generally desirable in the art of making smart labels and smartpackaging products to be able to measure the integral of temperature,humidity, or other variable over time. Such an integration measurementcan be used to indicate a degree of exposure to undesirableenvironmental conditions. Time-Temperature Integration (TTI) andTime-Humidity Integration (THI) are two such valuable metrics used todetermine product abuses or levels of freshness.

To accomplish such measurements, it is known in the art that a highdegree of accuracy can be obtained using an Analog to Digital Converter(ADC), together with a processing logic unit that performsfloating-point algorithms. Alternately, a microprocessor, a ProgrammableLogic Device (PLD) or a Digital Signal Processor (DSP) type ofprocessing platform can be used.

When considering the cost of goods required to build such processingcircuitry into smart labels and smart packages, even at the smallestlevels of integration (deep sub-micron), using fully custom ApplicationSpecific ICs (ASICs), the cost of goods is too high to be applicable ina typical packaging situation. Cost sensitivities drive the need forlower-cost and lower-power circuitry for smart label and smart packagingdevices.

SUMMARY

The circuit architecture and fabrication method of the presentapplication provides signal processing using an analog integrationmethod, with circuit elements built directly onto a substrate comprisinga polymer, such as, for example, Polyethylene (PET) or Polyamide.

It is understood in the art that circuit elements such as transistors,resistors, capacitors, LEDs, and high grade conductors can be fabricateddirectly upon PET substrates using ink-jet printing methods. Thisdisclosure applies these methods, in combination with the use ofsilicon-based circuits, to achieve a low-cost temperature and humidityintegration and indication circuits.

An analog circuit can drift and lose accuracy when used to measure theintegrated value of a variable (such as temperature or humidity) overlong periods of time. Due to tolerance problems with analog components,it is difficult to gain degrees of accuracy greater than about 0.1%using off-the-shelf chip resistors and capacitors. Parts of the circuitcan be tuned, and precision component tolerances can be specified, butat increased expense.

The apparatus disclosed in the present application can be trimmed bylaser cutting to achieve high accuracy. This, in combination with otheraspects of the sampling and counting methods used, result in an accuratemethod of performing the long-term integrations required to suit thesmart label and smart packaging applications.

In one embodiment, an integrator comprises a polymer substrate and anoperational amplifier comprising a first input terminal, a second inputterminal, and an output terminal. The integrator further comprises anaccumulator formed on the polymer substrate and connected between thefirst input terminal and the output terminal of the operationalamplifier.

In another embodiment, a system is disclosed for monitoringenvironmental conditions of a perishable product. The system comprisesan environmental sensor configured to sense one or more environmentalconditions of the perishable product and an analog integrator incommunication with the environmental sensor, the analog integrator beingformed on a polymer substrate and including one or more tunablecomponents. The system further comprises a comparator in communicationwith the analog integrator and configured to change state when an outputof the analog integrator reaches a selected threshold level, and acontrol module in communication with the comparator and the analogintegrator. The control module is configured to control the operation ofthe analog integrator based on an output of the comparator.

In another embodiment, a system comprises a humidity sensor coupled to afirst analog integrator and a temperature sensor coupled to a secondanalog integrator. The system further comprises a first comparatorcoupled to the first analog integrator and a second comparator coupledto the second analog integrator. The system further comprises ananalog-to-digital converter coupled to the humidity sensor and thetemperature sensor, and a control module coupled to the first and secondanalog integrators, the first and second comparators, and theanalog-to-digital converter.

In another embodiment, a method of tuning a system for monitoringenvironmental conditions of a perishable product comprises fabricating acapacitor comprising a first capacitive plate formed on an upper surfaceof a polymer substrate and a second capacitive plate formed on a lowersurface of the polymer substrate, the first and second capacitive platescomprising a capacitive plate material. The method further comprisesremoving capacitive plate material while measuring the capacitance ofthe capacitor until a selected capacitance is reached, and incorporatingthe capacitor into an analog integrator circuit configured to receive aninput signal from an environmental sensor capable of monitoring one ormore environmental conditions of the perishable product.

These and other embodiments of the present application will be discussedmore fully in the detailed description. The features, functions, andadvantages described herein can be achieved independently in variousembodiments of the present application, or may be combined in yet otherembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an integrator circuit in accordancewith one embodiment of the present application.

FIG. 2 is a timing diagram depicting the operation of the integratorcircuit shown in FIG. 1.

FIG. 3 depicts an isometric view of a capacitor in accordance with oneembodiment of the present application, shown with layers separated foridentification.

FIG. 4 is a schematic diagram of an environmental monitoring system inaccordance with one embodiment of the present application.

FIG. 5 is a schematic diagram of an environmental monitoring system inaccordance with an alternative embodiment of the present application.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific illustrative embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that various changes may be made without departing from thespirit and scope of the present invention. The following detaileddescription is, therefore, not to be taken in a limiting sense.

Depicted in FIG. 1 are the circuit elements of an analog integrator 100that provides sampling and integration of an input signal, V_(s),received from an environmental sensor, such as, for example, atemperature sensor or a humidity sensor. The integrator 100 preferablyallows precision measurement of low input currents that are accumulatedto an accurate total charge. In some embodiments, the integrator 100employs an operational amplifier 105 with a low input bias current. Thevalue of resistor R1 can be selected to set the gain of operationalamplifier 105 at a desired level.

Capacitor pair C2/C3 form an integrating capacitor (accumulator) thatstores charge at a greater or lesser rate, based upon the input currentof the operational amplifier 105. This accumulated charge, in turn,produces the output analog voltage level V_(o), according to thefollowing equation:

$V_{o} = {{- \frac{1}{C_{int}}}{\int{{I_{in}(t)}{{\mathbb{d}t}.}}}}$In this equation, C_(int) is the combined capacitance of C2 and C3, andI_(in) is the input current to the operational amplifier 105.

The arrangement and sequencing of analog switches S1 through S3 providescontrol of the integrator 100, as described below in connection withTable 1. In the illustrated embodiment, S1 is controlled by anintegration control signal, V_(int), S2 is controlled by a reset controlsignal, V_(r), and S3 is controlled by a charge control signal, V_(c).These control signals can be generated by any suitable control module,such as, for example, a logic circuit or a microcontroller. In theillustrated embodiment, the control signals are amplified by drivers110, 115, 120, which can be integrated into the analog switches S1through S3.

In some embodiments, capacitor C1 is of a small capacitance, e.g., tensof picofarads. When beginning from a discharged state, the chargevoltage of C1 quickly rises to the level of V_(s), the sensor voltage,whenever S3 is closed. When the integrator 100 is sequenced, the smallcharge from capacitor C1 is transferred to pair C2/C3. C2 is of a muchlarger capacitance than C1 or C3, e.g., on the order of tens ofmicrofarads. The C2/C3 pair can contain on the order of one-half to onemillion samples from C1 and still not be fully charged to the negativevoltage rail. In some embodiments, C3 comprises a trimming capacitor inparallel to C2. The function of C3 will be described further below.

Sensors can be connected in such a way as to sink or source current fromthe input terminal of the operational amplifier 105. This causes apositive or negative integration ramp voltage on C2/C3, accordingly. Theconfiguration shown in FIG. 1 sources current and thereby produces anegative integration ramp.

Table 1 below shows four operating states of the integrator 100.

TABLE 1 Integration States Step State S1 S2 S3 Description 1 4 0 0 1Charge C1 2 1 1 0 0 Transfer C1 charge to C2/C3 3 0 0 0 0 Off/Hold C2/C3R 2 0 1 0 Reset C2/C3

In typical operation, a series begins by charging C1 (Step 1),transferring the charge to C2/C3 (Step 2), then holding the charge for arelatively long period (Step 3) before taking another reading. In thisway, sparse samples can be taken, and their aggregate value accumulated.The output V_(o) can be sampled, or preferably it can be fed into acomparator circuit (not shown).

The comparator can be made to change state when V_(o) reaches a presetlevel, and this can trigger a Reset (Step R) of the integrator 100. Theoccurrence of the trigger event indicates a fixed aggregate level ofsensor input, which is proportional to net charge. When measuringtemperature, for example, a trigger event indicates that a certainnumber of net calories of heat have been measured.

FIG. 2 is a timing diagram showing the operation of the integrator 100illustrated in FIG. 1. As illustrated in FIG. 2, V_(o) drops slightlywith each transfer of energy from C1. In the figure, FS and −FSrepresent the full-scale values of V_(C1) and V_(o), respectively. Ifthe sensor voltage, V_(s), is lower due to a lower temperature, then theintegration rate will be slower.

In some embodiments, capacitors C1 and C3 are constructed in a mannersuch that their capacitance can be precisely set in a high-speedfabrication process. C1 and C3, if trimmed to accurate capacitancevalues, will provide a reliable basis for aggregate measurement of anintegral of sensor output level.

FIG. 3 depicts an isometric view of a capacitor 300 in accordance withone embodiment of the present application, shown with layers separatedfor identification. The exemplary capacitor 300 can be constructed foruse as C1 or C3 in the integrator 100 of FIG. 1. In some embodiments,capacitor 300 comprises an upper capacitive plate 305 and a lowercapacitive plate 310 separated by a dielectric layer 315. The capacitiveplates 305, 310 may comprise any suitable capacitive material, such as,for example, metal. In some embodiments, the capacitive plates 305, 310comprise conductive material formed as layers of laminated, metallizedpolyester film, such as, for example, Mylar®. The polyester film can bemetallized with any suitable metal, such as, for example, aluminum,silver, gold, etc. Dielectric layer 315 may comprise any suitabledielectric material, such as, for example, PET, polyamide,polypropylene, etc.

In some embodiments, capacitor 300 can be built using a die-cut,roll-to-roll sheet lamination process, in which capacitor 300 can alsobe trimmed to a set capacitance via a closed-loop capacitor tuningprocess. In such a process, plate material is removed as measurementsare made in real-time, until the capacitance falls to a given targetcapacitance. Typically, a capacitance measurement instrument isconnected across the capacitive plates 305, 310 and a cutting devicesuch as a robotic laser is positioned and activated to remove preciseamounts of aluminum. Further measurements and smaller cuts/holes aremade until the desired capacitance is reached. Capacitive sheets mayalso be pleated and stacked on top of one another to increase totalcapacitance, and trimmed to set values in a similar manner. As a resultof establishing a precise capacitance for capacitor 300, the accuracy ofthe integration that the integrator 100 illustrated in FIG. 1 canperform is advantageously improved.

By using the circuit construction and methods described above in a smartpackage or smart label product, it is possible to reduce the complexityof the silicon circuitry and to provide features of a circuit directlyon a polymer substrate, such as, for example, PET, Mylar®, polyamide,etc. The electronics that can be printed and/or laminated includesensors, resistors and capacitors. The adaptation of a precisionintegrator using printed and laminated components provides a higherdegree of benefit in its accuracy at lower total cost, as compared toconventional circuits, which consist of silicon-based circuits plusthick-film passive components that are soldered onto printed wiringboards.

Some of the materials used in printing electronic components onsubstrates are as follows: (a) conductors: organic inks such as PEDOTand Polyanilene (PAni) conduct electron current effectively(approximately 100 S/cm conductivity); (b) semiconductors: conjugatedpolymers such as Poly-3-alkylthiophene (P3AT) Polythiophene andPoly(3-hexylthiophen) can be dispensed in a solution form, as used insemiconductive inks; (c) insulators/barriers: insulating polymers, suchas PMMA, are used for insulation layers and/or barrier formation.Sensors can be constructed from metallic (such as silver) sensingcompounds that are deposited between two conductive electrodes on thesubstrate. All of these chemicals can be formulated into inks to besprayed from ink-jet nozzles or plotted via micro-pen onto Polyethylene(PET) substrates at room temperatures, in semi-clean or cleanenvironments.

FIG. 4 is a schematic diagram of an environmental monitoring system 400in accordance with one embodiment of the present application. In theillustrated embodiment, the integrator 100 comprises one or more tunablecomponents 430, such as capacitor 300 described above. In operation,integrator 100 receives an input signal, V_(s), from an environmentalsensor 435 and provides an output signal, V_(o), to a comparator 405.When a comparison target level is reached, a logic circuit 410 sends areset control to the integrator 100 and at the same time tallies thecount of thresholds that were reached. When a target number of thresholdcounts are reached, the indicator drivers 415 can drive alarmindications to the display 420 or audio emitter 425. A battery andvoltage converter (not shown) can be used to supply power to the system400.

FIG. 5 is a schematic diagram of an environmental monitoring system 500in accordance with an alternative embodiment of the present application.In the embodiment illustrated in FIG. 5, system 500 comprises twointegrators 100A, 100B, each of which includes one or more tunablecomponents 560A, 560B, such as capacitor 300 described above. The firstintegrator 100A is used to integrate the sensor voltage of a humiditysensor 505, and the second integrator 100B is used to integrate thesensor voltage of a temperature sensor 510. The system 500 furthercomprises a microcontroller 515 that receives inputs from the outputs ofthe two comparators 520A, 520B, and also receives input from atwo-channel ADC 525 that monitors each sensor 505, 510 directly. System500 is capable of programmatic control of integration and of indicatordrivers 530, which can drive alarm indications to the display 535 oraudio emitter 540. System 500 is also capable of programmatic control ofsuch peripheral devices that can also be incorporated into the smartlabel or package, such as, for example, a data transceiver 545, areal-time clock 550, and/or a non-volatile memory 555. A battery andvoltage converter (not shown) can be used to supply power to the system500.

The systems and methods described above can be used to monitorenvironmental conditions of a wide variety of perishable products, suchas meat, poultry, seafood, dairy products, cosmetics, chemicals, etc.These systems and methods can advantageously be incorporated intovarious labels, tags, packages, and/or packaging materials used inconnection with such perishable products. As described above, thesesystems and methods can lead to significant cost savings overconventional circuits used in existing smart packaging and/or smartlabeling products.

Although this invention has been described in terms of certain preferredembodiments, other embodiments that are apparent to those of ordinaryskill in the art, including embodiments that do not provide all of thefeatures and advantages set forth herein, are also within the scope ofthis invention. Accordingly, the scope of the present invention isdefined only by reference to the appended claims and equivalentsthereof.

1. A system comprising: a humidity sensor coupled to a first analog integrator; a temperature sensor coupled to a second analog integrator; a first comparator coupled to the first analog integrator; a second comparator coupled to the second analog integrator; an analog-to-digital converter coupled to the humidity sensor and the temperature sensor; and a control module coupled to the first and second analog integrators, the first and second comparators, and the analog-to-digital converter.
 2. The system of claim 1, wherein the first and second analog integrators include one or more tunable components.
 3. The system of claim 1, wherein the first and second analog integrators are fabricated on a polymer substrate.
 4. The system of claim 1, wherein the control module comprises a microcontroller.
 5. The system of claim 1, further comprising one or more indicator drivers coupled to the control module.
 6. The system of claim 5, further comprising a display and/or audio emitter coupled to the indicator drivers.
 7. The system of claim 1, further comprising a transceiver, real-time clock, and/or non-volatile memory coupled to the control module. 